A recent significant advancement in the field of post-mixed spark-ignited burners is the development of an ignition system wherein the burner itself comprises the sparking means. This ignition system is described and claimed in U.S. Pat. No. 4,431,400, issued Feb. 14, 1984. In this ignition system a conduit carrying fuel or oxidant is electrically conductive and electrically isolated from another conduit carrying the fluid not carried by the first conduit. Both conduits end at the discharge end of the burner and are arranged such that the point of lowest breakdown voltage between them is also at the discharge end. When electrical potential is applied, a spark discharges between the two conduits at the discharge end igniting the fuel and oxidant.
The above-described ignition system is very safe and reliable as well as being relatively simple to manufacture and maintain. However this ignition system mandates a number of aspects which require precision or else the ignition system will fail to work properly resulting in the loss of safety, reliability and/or simplicity.
First, the two conduits must at all points be electrically isolated from one another and the point of lowest breakdown voltage must at all times be at the burner discharge end. This requires that the position of the two conduits relative to one another, both axially and radially, be fixed. Any significant movement of one conduit relative to the other may cause spark to form at other than the burner discharge end. Movement may be caused by external force such as may be applied by the supply conduits. This problem of rigid relative fixation combined with total electric isolation is more difficult when the conduits are concentric, i.e., when one conduit is within the other conduit.
Second, the central conduit must be able to be supplied with fluid without compromising either its electrical isolation or its physical position. It is also desirable that the central conduit be supplied with electrical potential so that spark arcs from the central to the outer conduit and all exposed outer housing be electrically grounded to minimize any safety hazard to the burner operator. Thus the central conduit must be able to be supplied with electricity without compromising either its electrical isolation or its physical position.
Third, the burner being a post-mixed burner wherein the fluid in the central conduit must not mix with the fluid in the outer or annular conduit until they are both discharged out the discharge end of the burner, the fluid must be supplied to the central conduit such that mixture with fluid in the annular conduit is prevented while maintaining the required electrical isolation and physical positioning.
Fourth, the burner assembly to satisfy the above-described requirements should be relatively simple. A complicated system would negate the benefits of the simplicity of the aforementioned ignition system. A complex assembly would also make periodic disassembly of the burner for cleaning or parts replacement an unduly time consuming and expensive task.
It is therefore an object of this invention to provide an assembly for a post-mixed spark-ignited burner which effectively electrically isolates a central conduit from an annular conduit.
It is another object of this invention to provide an assembly for a post-mixed spark-ignited burner which effectively fixes the position of the central conduit relative to the annular conduit.
It is a further object of this invention to provide an assembly for a post-mixed spark-ignited burner wherein the central conduit is effectively supplied with fluid and with electrical potential without compromising the required electrical isolation and physical positioning.
It is a still further object of this invention to provide an assembly for a post-mixed spark-ignited burner wherein fluid intended to flow through the central conduit is effectively prohibited from mixing with fluid intended to flow through the annular conduit until they are both discharged from the discharge end of the burner.
It is yet another object of this invention to provide an assembly for a post-mixed spark-ignited burner which effectively accomplishes the above-described objects while also being relatively simple and which allows for facile disassembly and reassembly.